Penetration-bonded metal composition for power-breaker contacts



Jan. 13, 1970 H. SCHREINER 3,489,530

PENETRATION-BONDED METAL COMPOSITION FOR POWER-BREAKER CONTACTS Filed July 16, 1968 2 Sheets-Sheet 1 TU Em IAs ECopper j .0

20 Invesiigated Range Tungsten 1U (sintered) V H g/cm Fig.1

W 20 L0 B0 Bl] 100 VOL- le F|g.2

Jan. 13, 1970 H. SCHREINER 3,489,530

PENETRATION-BONDED METAL COMPOSITION FOR POWER-BREAKER CONTACTS Filed July 16, 1968 2 Sheets-sheaf; 2

United States Patent 3,489,530 PENETRATION-BONDED METAL COMPOSITION FOR POWER-BREAKER CONTACTS Horst Schreiner, Nuremberg, Germany, assignor to Siemens Aktiengesellschaft, a corporation of Germany Continuation-impart of application Ser. No. 640,543,

May 23, 1967. This application July 16, 1968, Ser. N 0. 752,094 Claims priority, application Germany, June 3, 1966,

Int. Cl. B22t1/00, 5/00 US. Cl. 29-1821 1 Claim ABSTRACT OF THE DISCLOSURE This is a continuation-in-part of my application Ser. No. 640,543, filed May 23, 1967 and relates to penetration-bonded metal compositions for use as arc-resistant contact material in power circuit breakers including those operating at high voltages, such as line voltages of 110 or 220 v., or at considerably higher voltages, now abandoned.

The contact pieces which in high-voltage power breakers become subjected to the current-interrupting are have been made of penetration-bonded metal compositions formed of tungsten and copper. A penetration-bonded composition is constituted by a skeleton of the refractory metal component (tungsten) which has the voids in the skeleton structure impregnated and filled with the lowmelting metal component (copper). The shaped workpieces are produced by compression oftungsten powder, or by pressing a powder mixture of tungsten and copper, or a mixture of tungsten, copper and nickel. The shaped mixture is then sintered, and the resulting skeleton is thereafter impregnated with copper. As a rule, the density of a penetration-bonded metal composition, made by pressing a skeleton-forming component, namely tungsten, and impregnating the sintered skeleton structure with copper, is above 13.0 g./cm. Shaped workpieces of such materials, such as arcing contacts, exhibit a considerably smaller amount of consumption due to interrupting arcs, particularly in high power breakers operating in air, or in oil or other arc-extinguishing liquids such as sulfur hexafluoride (SP Attempts have been made to further reduce the consumption of such contact materials due to exposure to interrupting arcs.

The production of shaped contacts and the like workpieces from the known penetration-bonded metal composition is expensive and the economy of such production is considerably affected by the relatively large amount of material-removing machining that must be applied to the shaped green bodies. There is another known modification of the method according to which the production of such compositions is performed by using a poured quantity of tungsten powder and impregnating it with copper; but the products thus obtained fail to secure a satisfactory high resistance to wear under arcing conditions. A penetration-bonded composition of the latter type, while having a lower density than 13.0 g./cm.

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possesses too small a strength of its skeleton structure, and this leads to relatively high amounts of burn-off.

It is an object of my invention to provide a penetration-bonded metal composition suitable for the abovementioned use in circuit breakers or for other purposes requiring resistance to arcing or similarly high temperatures, that greatly reduces the above-mentioned shortcomings of the known compositions.

The penetration-bonded metal composition according to the invention consists of a copper-impregnated, sintered skeleton structure of tungsten-copper-nickel, having a density of 11.0 to 13.0 g./cm.

This composition is produced by shaping a powder mixture of tungsten, copper and nickel under pressure to the desired shape of the contact or other workpiece, then sintering the shaped body, and subsequently impregnating it with molten copper. Due to the sintering process involving a liquid phase, the resulting skeleton structure is given a high mechanical strength at high temperatures (measured at 800-1000 C.), this being due to the formation of tungsten-tungsten bridges between the powder particles. The advantage of the tungsten-copper sinter structure resides in the slight burn-off of the penetration-bonded composition made from such a structure, the burn-off consumption being less than with a bonded composition of substantially the same composition but having the skeleton structure produced of tungsten and copper. It has been found preferable to produce the sintered skeleton structure of compositions according to the invention from sinter-active tungsten powder to which is added an amount of 1-10% by weight of copper and 0.010.2% of nickel.

Contacts made of a penetration-bonded composition according to the invention are distiguished mainly by their high-temperature strength and the cavity-free impregnation of the skeleton structure, and by a considerably lesser amount of wear due to arcing as compared with the previously known penetration-bonded metal compositions having a density within the same range. This appears to be due to the phenomenon that the tungsten-coppernickel penetration-bonded composition according to the invention happens to conjointly exhibit favorable physical, chemical and electrical properties, especially when operating under oil, so that the minimum of burn-off occurs at a density of about 12 g./cm. This is apparent from the diagram of FIG. 1 to be more fully discussed hereinafter. Another essential advantage resides in the fact that finished workpieces. having the ultimate shape and dimensions, as well as good external contours, can be obtained without subsequent processing. This is manifested by the following example.

When producing a tungsten-copper penetration-bonded metal composition whose sintered skeleton structure contains nickel within the limits of 0.01 to 0.2% by weight, a very slight amount of shrinkage is observed when sinter ing the skeleton structure. The subsequent impregation of this sintered structure with copper also involves slight additional shrinkage only. As a result, a shaped contact or other workpiece is obtained whose density is between 11.0 and 13.0 g./cm. and whose shape and dimensions are sufficiently accurate to permit doing away with chipremoving or material-removing work, or reducing such work to a minimum. For that reason a considerable economical advantage is also attained over the methods and compositions of this type heretofore available.

Another advantage is the good soldering and welding ability of the penetration-bonded composition according to the invention, relative to the conventional carrier or mounting metals employed for holding such contacts.

The invention will be further described with reference to the accompanying drawings in which:

FIGS. 1 and 2 are explanatory diagrams representing 3 measuring results. obtained with comp to..the..invention. F.

FIGS. 3 to 6 show in cross section four different embodiments of contact pieces made according to the invention.

A contact of a penetration-bonded metal composition accordingto theinvention can be produced as follows. The .pulverulent mixture 1 (FIG. 3) or.1.' (FIG. 4) from which the skeleton structure is to be formed is placed into a die or'mold 2 or 2 of ceramic material. This is done either by shaking the powder into the mold -or by pressing the powder in the mold. The dimensions of the mold are such that they slight shrinkage due to subsequent sintering is taken into account, such shrinking amounting up to 1%. The mass of powder thus shaped inside the mold is then sintered within the mold by subjecting the mold to a temperature between 1200 and 1500 C. in hydrogen or vacuum. When applying a sintering temperature above 1300 C., it is preferable to first presinter the body at about 1000 C. and to continue the sintering process after the skeleton structure has been removed from the mold. The sintering time is so chosen that a maximal skeleton strength is attained for the given space filling degree. After sintering or pre-sintering, the sintered skeleton structures will drop out of the mold when the mold is turned upside down. The quantity of copper required for impregnating the skeleton structure and for completely filling its pores or voids is applied as a pressed part consisting of electrolysis copper. This copper part is placed onto or beneath the skeleton structure. The assemblage is then heated in a mold of graphite or ceramic for to minutes at an impregnating temperature about equal to the melting point of copper. Preferably applied is an impregnating temperature of 1200 to 1350 C. During impregnation there occurs a slight additional shrinkage of the shaped skeleton structure amounting to approximately 0.5%. After impregnation, the shaped workpiece corresponds to the described dimensions and its contours need not be machined by material-removing tools.

FIG. 3 relates to the production of a body of rotation having generally the shape of a plug; and FIG. 4 relates to the production of a workpiece in the shape of a circular ring.

FIG. 5 shows the finished contact piece 1 according to FIG. 3 provided with a ring 3 of brazing material which in this case is placed upon a machined neck of the contact piece and serves to join it with a carrier metal.

FIG. 6 shows the finished ring-shaped workpiece 1' with a ring 3' of brazing material on a peripheral shoulsitions according der, also serving to hard-solder or braze the contact piece to a -supporting metal structure.

The diagrams shown in FIGS. 1 and 2 are illustrative of the above-mentioned progress achieved by virtue of the invention. FIG. 1 relates to the amount of Wear (burn-off) due to arcing as it occurs with a tungsten-copper-nickel penetration bonded composition according to the invention-The ordinate indicate's'thea'mo'unt of material burned away by arcing, this amount being fshow n 'in units of 10 cmF/as. (amp second} The abscissa indicates the density of the composition in g./crn., It will be noted that the amount of wear has a minimum in the neighborhood of the density 12.

The diagram shown in FIG. 2 illustrates the relation between the composition and the density of tungsten-copper penetration-bonded compositions. The ordinate indicates the density in g./cm. and the abscissa the com position in volumetric percent or weight percent. The small percentage of nickel, amounting to 0.010.2% by weight, is not separately considered in FIG. 2 because of the slight difierence in density (nickel: density=8.8 g./ cm. copper: density=8.93 -g./cm. The space filling degree of the skeleton structure is indicated as a parameter for each of the individual curves shown.

I claim:

1. A penetration-bonded metal composition suitable a arc-resistant material in high-voltage power breakers, consisting substantially of a copper-impregnated, sintered skeleton structure of tungsten-copper-nickel having a density of 11.0 to 13.0 g./cm. said skeleton structure consisting essentially of 1 to 10% by weight of copper, 0.01% to 0.2% of nickel, the remainder being substantially, all of tungsten.

References Cited UNITED STATES PATENTS 2,986,465 5/1961 Kurtz 212 3,360,348 12/ 1967 Schreiner 2 9-182.2 X 3,366,463 1/1968 Schreiner 29 182.2 X

FOREIGN PATENTS 836,749 6/ 1960 Great Britain.

CARL D. QUARFORTH, Primary Examiner ARTHUR I. STEINER, Assistant Examiner US. Cl. X.R. 75-208 

